Perishable products have measurable shelf-lives, which are usually expressed within specified limits as the time left for available end use. The term “perishable(s)” or “perishable product(s)” is meant herein to include perishable foods, such as fresh, refrigerated, and frozen, vegetables, fruits, meats, fish, poultry, dairy products, bakery products, juices, pre-cooked foods, soft and alcoholic beverages, and also including nonfood items having shelf lives ranging from a few hours to several years including pharmaceuticals, vaccines, sera, blood, blood plasma, cosmetics, reactive chemical compounds, bio-chemicals, bio-products, and batteries which have a measurable shelf life.
Whenever a clock or timer is impractical or too expensive to use, color changing time indicators or indicating devices in forms of labels, stickers or badges are used. Indicators for monitoring the passage of a relative amount of time are referred herein to as time indicator (TI) or time indicating device including but not limited to visual validation of time, safety sticker, self-timing retail sticker, biological industrial process monitoring, self-expiring stickers to prevent re-use, employee ID and security ID labels, visitors badges, self-expiring parking tags, package and shipping labels, wrist bands, time indicating tickets for trains, buses, sport events, theaters etc., self-expiring passes for tours, emergency rooms, hospitals, museums, and other locations, event passes, security labels for screened luggage, purses, bags at airports to show the aircraft control people that the particular items were inspected, unmanned but video controlled entrances for visitors where the self-expiring visitor label issued electronically. It also includes limited use items for consumers where once opened or in use should be used within certain period, including but not limited to drinks, food items, health, personal and family care products.
Time-temperature indicator(s) (TTI) devices provide a way of indicating a cumulative exposure to time and temperature. A TTI device may be capable of indicating whether a commodity has been exposed to a temperature greater than a predetermined temperature for a period of time or to an integral value of time and temperature. For example, a TTI device might indicate exposure to an excessive temperature for an excessive period of time or both. A large number of time-temperature indicating devices and time indicating devices for monitoring thermal degradation of perishables and self-expiring labels, tickets and badges have been reported in patent literature. Many of these devices are based on diffusion of a chemical from one matrix to the other, sometimes through a permeable layer, to introduce a color change in the indicator layer. The other TTIs are based on chemical reactions, such as the solid state polymerization of diacetylenes, change in pH and change in photochromism and thermochromism.
A large number of patents have been issued for devices that monitor time and integral value of time and temperature.
Patel, in U.S. Pat. No. 5,053,339 discloses a color changing device for monitoring the time-temperature storage history, i.e. shelf life of perishable products. The device is composed of (1) an activator tape, containing an activator composition and matrix on a substrate, (2) an indicator tape, containing an indicating composition, matrix and (3) an optional permeable layer. The permeable layer is often referred to as a barrier layer. The device is activated by applying the activator tape over the indicator tape. This and similar devices in general are often referred herein to as two-tape devices, two-tape TTI and TI.
Haas and his co-inventors in a series of U.S. Pat. Nos. 4,903,254; 5,053,339; 5,446,705; 5,602,804; 5,633,835; 5,699,326; 5,715,215; 5,719,828; 5,785,354; 5,822,280; 5,862,101; 5,873,606; 5,930,206; 6,446,865, 6,452,873; 6,752,430; 7,139,226; and 7,263,037 have disclosed time monitoring devices and related processes. These devices are also based on diffusion of an activator (which also includes a dye) through a medium. The indicator has a matrix, e.g., an ink which has a binder.
The following patents are some other representative examples of TI and TTI devices: U.S. Pat. Nos. 2,896,568; 3,018,611; 3,046,786; 3,078,182; 3,311,084; 3,520,124; 3,921,318; 3,954,011; 3,962,920; 3,999,946; 4,154,107; 4,195,058; 4,212,153; 4,382,063; 4,404,922; 4,432,630; 4,432,656; 4,448,548; 4,480,749; 4,542,982; 4,573,711; 4,629,330; 4,643,122; 4,643,588; 4,646,066; 4,737,463; 4,779,120; 4,812,053; 4,846,095; 4,846,502; 4,917,503; 5,053,339; 5,058,088; 5,120,137; 5,293,648; 5,317,980; 5,364,132; 5,378,430; 5,446,705; 5,602,804; 5,633,836; 5,667,303; 5,699,326; 5,709,472; 5,715,215; 5,719,828; 5,785,354; 5,822,280; 5,862,101; 5,873,606; 5,930,206; 5,957,458; 5,974,003; 5,997,927; 6,042,264; 6,103,351; 6,214,623; 6,254,969; 6,514,462; 6,524,000; 6,536,370; 6,614,728; 6,752,430; 6,822,931; 6,916,116; 7,156,597; 7,157,048; 7,209,042; 7,280,441; 7,290,925 and 7,294,379.
Pre-cooked, ready-to-eat frozen foods are widely used today. The pre-cooked frozen food is heated either in a conventional oven (for example, heated with natural gas or electricity) or more conveniently in a microwave oven. A microwave oven does not heat the food uniformly. Some portions of food may not be done while the other portions may be over heated. Hence, there is a need for an indicating device that changes color when steam is emitted by the food.
There are a variety of threshold and defrost indicating devices reported in the literature, including those in the following patents: U.S. Pat. Nos. 3,233,459; 3,702,077; 3,786,777; 4,038,936; 4,114,443; 4,120,818; 4,144,834; 4,163,427; 4,280,361; 4,735,745; 4,892,677; 5,267,794; 5,685,641 and 5,695,284. This type of indicating devices undergo a color change with time and temperature when the product temperature undesirably exceeded above a pre-determined temperature, e.g., about 0° C. These devices have not proven entirely satisfactory due either to deficiencies in their visual perceptual character or in the danger of their use, in their sensitivity to thawing conditions or in their complexity of manufacture or use. The shortcomings of such devices are that they often fail in practice.
A wide variety of medical supplies and other items are sterilized with materials and techniques, such as steam, dry heat, ethylene oxide, plasma, peracetic acid, formaldehyde and high-energy radiation. Kitchenware, such as dishes, cutlery, and utensils used at home and restaurants are also sterilized in dishwashers with hot water and hot air usually around 90° C. It is essential to assure that these items are sterilized or meet required specifications. A number of sterilization indicating devices, dosimeters and monitors are proposed in the literature. They include biological and chemical indicating devices. The color changing chemical indicating devices are inexpensive and are widely used.
A wide variety of foods especially canned foods, pharmaceuticals, hospital and medical supplies are sterilized. These and other products, such as linens are sterilized to kill living organisms to an acceptable level. Direct testing for sterility is destructive and expensive and hence indirect testing methods, such as color changing indicating devices are used.
Pressurized steam is used in hospitals to sterilize reusable medical equipment and supplies, such as gowns and linens. To differentiate between a tray containing sterilized goods and one containing non-sterile goods, which may not have been processed, an indicating device is used. The process of sterilization causes the device to change color. Often the original color is light, and the color after processing is dark. The change in color is caused by a chemical reaction in the ink. The indicating device may be in the form of a strip, card, or tape. By observation of the color of the sterilization indicating device, one can determine whether or not the package has been passed through the sterilization cycle.
Many steam sterilization indicating devices are reported in the literature and some of them are used for monitoring sterilization. A few of them use heavy and toxic metal compounds, such as those of lead or bismuth. For example, U.S. Pat. No. 3,523,011 describes an indicating device material consisting of calcium sulfide and lead carbonate. A number of patents are issued based on color changing sterilization indicating devices (e.g., those for steam, dry heat, ethylene oxide, plasma, peracetic acid, formaldehyde and high-energy radiation) using inorganic and organic compounds, including a variety of dyes and pigments. They include the following U.S. Patents: U.S. Pat. Nos. 2,798,885; 2,826,073; 3,098,751; 3,360,337; 3,360,338; 3,360,339; 3,386,807; 3,471,422; 3,568,627; 3,852,034; 3,862,824; 3,932,134; 3,981,683; 4,094,642; 4,121,714; 4,138,216; 4,195,055; 4,407,960; 4,410,493; 4,436,819; 4,486,387; 4,514,361; 4,576,795; 4,579,715; 4,596,696; 4,692,307; 4,678,640; 5,064,576; 5,087,659; 5,158,363; 5,200,147; 5,223,401; 5,252,484; 5,258,065; 5,451,372; 5,788,925; 5,801,010; 5,866,356; 5,916,816; 5,990,199; 6,063,631; 6,485,978; 6,589,479; 6,659,036; 6,800,124; 6,884,394; 7,141,214 and 7,189,355.
Many of the above mentioned devices are also based on vertical diffusion of a liquid or vapor through a permeable barrier which is usually very thin, typically less than 100 microns.
Thin layer chromatography (TLC) is a chromatography technique used for separation of a non-volatile mixture of compounds, often referred as analytes. Thin layer chromatography is performed on a substrate material, such as a sheet of glass, plastic, or aluminum foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminum oxide or cellulose. This layer of adsorbent and/or absorbent is known as the stationary phase (SP). After a sample of analytes has been applied on the plate, a solvent or solvent mixture, known as the mobile phase (MP) is drawn up the plate via capillary action or wicking. Because different analytes ascend the TLC plate at different rates, separation is achieved.
Moving boundary devices for monitoring variety processes such time-temperature and sterilization based essentially on principal of TLC are proposed. They include the following:
U.S. Pat. No. 3,479,877 discloses an indicator device for showing the length of time an environment has been at or above a predetermined temperature. A fusible tablet of temperature indicator substance enclosed by a protective rigid cap is positioned at one end of a wick which is attached to but spaced from a heat-conducting base sheet. When the predetermined temperature is reached, the indicator substance melts and flows along the wick, the distance of flow indicating the length of exposure time.
U.S. Pat. No. 3,981,683 discloses a sterility indicator comprising a backing strip of a dimensionally stable material e.g. aluminum foil having mounted thereon an organic compound containing oxygen or nitrogen in intimate contact with a wicking means and a cover strip bonded to the backing strip overlaying the organic compound and wicking means. The cover strip is a polymeric rate controlling film which permits water vapor to pass through at a rate sufficient to make the device operative at a temperature to be monitored
U.S. Pat. No. 4,044,707 discloses a time-temperature indicator comprising: a fluid source and an interruptible wick in contact with said fluid source upon activation of said time-temperature indicator, said wick being interruptible through severance at a weakened area after activation of said indicator, and said fluid source containing an indicating substance which has a defined melting range and a set rate of migration along said wick when melted and after activation of said indicator
U.S. Pat. No. 4,353,990 discloses a device for monitoring thermal energy input and displaying the relationship of the thermal energy input to a selected time/temperature relationship. The device employs an indicating material which, when melted, expands and flows into a narrow channel to provide an irreversible, visible indication of the thermal energy to which the device has been exposed.
U.S. Pat. No. 4,382,700 discloses an indicator comprising a material, as for example a mineral jelly, which is in contact with a wick, such as a paper strip, such that the mineral jelly diffuses into the paper in accordance with changes in ambient temperature over a period of time. The amount of diffusion is indicated by an apparent change in color of the paper and is analogous to a change in the useful characteristic of the perishable goods.
U.S. Pat. Nos. 4,195,055 and 4,195,057 describe a vapor-phase moving-boundary indicator which is useful for monitoring the time-temperature histories of perishable articles. The device functions by allowing a vapor to permeate through a porous substrate coated with an indicating solid which undergoes a color change upon contact with the vapor. As the vapor permeates through the substrate, a visible moving boundary is created between two colors and it advances as a function of time and temperature. This provides a visual record of the time-temperature exposure of the article. In this case SP is coated but coated with solid and SP still remains porous.
U.S. Pat. Nos. 4,195,056 and 4,195,058 describe a time-temperature indicator (t-T indicator) which is constructed of a vapor-permeable barrier positioned between a vapor and an indicator, both housed in a vapor-impermeable container. The device is activated just prior to the monitoring period by providing vapor to the container, as for example, by rupturing a solvent-filled frangible reservoir. The indicator, upon contact with the vapor produces a visual color response, and the vapor is constrained to permeate through the vapor-permeable barrier before contacting the indicator, thus creating a characteristic induction period before a color response occurs. In this case SP is coated but coated with solid and SP still remains porous.
U.S. Pat. No. 4,410,493 discloses an indicator device which comprises a backing member, an indicator chemical, such as sebacic acid, which has the capability of wicking through a wick material, wicking means having one end of said wicking means in physical contact with said indicator chemical, said indicator chemical and wicking means being contained within a polypropylene envelope with the top and bottom interfaces of said envelope being sealed together to mechanically bond the wicking means and indicator chemical at the film envelope interfaces.
U.S. Pat. No. 4,448,548 discloses a steam sterilization indicator comprising a fusible material, in tablet form, deposited in an embossment in one end of a thin aluminum backing. A wicking strip is attached to the backing with one end of the strip being in close proximity to the fusible tablet. A clear plastic material covers the tablet and the strip and is adhered to the backing. The melting point of the fusible tablet is depressed in the presence of saturated steam. Upon melt, the material in the tablet is absorbed by the wicking strip, producing a color front to provide an indication of the integration of time and temperature in the presence of steam.
U.S. Pat. No. 5,045,283 discloses a moving boundary device constructed of an activator tape, containing an activator composition in an activator matrix, an indicating tape, containing an indicating composition in an indicator matrix in which the matrices are adhered together to form a wedge-shaped composite matrix, preferably by means of a pressure sensitive adhesive. The color change appears as a moving boundary at the color/non-color interface which moves transversely along the length of the device toward the thicker end of the composite matrix. The diffusion of the activator is vertical.
U.S. Pat. No. 5,180,598 discloses a liquid activated indicators comprising a porous structure which generates a first color by effects which include optical interference when pores of the structure are gas-filled, and a second contrasting color when the pores of the structure are liquid filled. The porous structure is covered with a transparent or translucent cover which is unattached in certain areas to allow for capillary movement of liquid between the cover and the porous structure. An entrance permits liquid to enter between the cover and the porous structure. When contacted with liquid, the liquid is drawn into the device and produces an expanding area of contrasting color which is used to indicate the elapse of time.
U.S. Pat. No. 5,723,336 discloses an indicator comprises a base substrate and two transparent polymeric layers on top of the base substrate in adhesive contact with each other. The indicator further comprises a valve member which is restrictive of the flow of dye therethrough, which valve is interposed between the two polymer layers such that there is no adhesive contact between the two polymer layers in the area of the valve. A deposit of colored dye is either on the lower polymeric layer, in which case the valve may be in physical contact with the dye, or on the base substrate. In either case the dye is visible through the polymeric layers, with the dye being positioned directly below the valve member, however, so that the valve member at least partially obstructs visibility of the dye deposit.
U.S. Pat. No. 7,232,253 discloses a time indicator comprising a first reservoir, a migration medium and activating means for bringing liquid from the first reservoir in contact with the migration medium so that after activation the liquid migrates through the migration medium producing a color change therein, characterized in that the activating means comprises a second reservoir connected between the first reservoir and the migration medium whereby after activation the liquid travels relatively rapidly from the first reservoir to the second reservoir and then migrates relatively slowly along the length of the migration medium over time; wherein the second reservoir is in the form if an inflatable pocket which inflates after activation.
U.S. Pat. No. 7,280,441 discloses a timer indicator or chronograph comprising: an indicator panel having a region with a number of visually distinct sections arrayed spatially relative to each other, said visually distinct sections each having at least one colorant different from an adjacent section, and having at least a reservoir containing an activating agent that constitutes a mobile phase that interacts with said indicator panel, and which transports said colorant along said indicator panel at a rate less than a rate of progression of said mobile phase for monitoring relative passage of time, and said reservoir being in controlled communication with said indicator panel.
U.S. Pat. No. 7,517,146 discloses an excess temperature indicator can provide a visual indication of past exposure of perishable, maturing and other host products to an elevated temperature exceeding a threshold temperature. The indicator can have an upper layer provided with a viewing window and a wick attached to the upper layer. A reservoir of heat-fusible indicator material can be disposed in contact with the wick, to fuse and move along the wick changing the visual appearance of a first portion of the wick viewable through the window, in response to an excess temperature event.
U.S. Pat. Nos. 7,562,811; 8,091,776 and 8,196,821 disclose a quality management system for products comprising: a multiplicity of product unit specific indicators each operative to provide a machine-readable indication of exceedance of at least one threshold by at least one product quality determining parameter, said machine-readable indication comprising a variable bar code having a first readable state and at least a second readable state, said first readable state and said at least a second readable state extending along a single axis, each readable state including digital indicia and at least start and stop code indicia, at least two digital indicia being different between said second readable state and said first readable state, wherein at least one of said start and stop code indicia which appear in said first readable state form part of said digital indicia in said second readable state and said second readable state includes additional indicia that appear at least one of before the digital indicia and after the digital indicia when the exceedance occurs; an indicator reader operative to read said product unit specific indicators and to provide output indications; and a product type specific indication interpreter operative to receive said output indications and to provide human sensible, product unit specific, product quality status outputs.
US Pat. Application No. 20120079981 discloses a temperature-activable time-temperature indicator that can be used to monitor the historical exposure of a host product to ambient temperatures includes an optically readable, thermally sensitive indicator element. The indicator element can be inactive below a base temperature and is intrinsically thermally responsive at or above an activation temperature which is equal to or greater than the base temperature. The indicator can record cumulative ambient temperature exposure above the activation temperature irreversibly with respect to time. The indicator element can include a synthetic polymeric material, and optionally, a dye. A side-chain crystallizable polymer, such as poly(hexadecylmethacrylate) that is solid below the base temperature and is a viscous liquid above the activation temperature can be employed.
US Pat. Application No. 20120236900 discloses a time-temperature indicator comprising: an indicator liquid reservoir; a migration medium; and a trigger; wherein the trigger is operable to release an indicator liquid from the reservoir upon activation of the trigger into an entrance of a channel defined within the migration medium, wherein the extent of migration of indicator liquid from the trigger area through the channel can be determined by a change in color or brightness of the migration medium and is an indication of one or both of differences in temperature and a passage of time; wherein the migration medium comprises a planar medium, having first and second major surfaces, which can absorb the indicator liquid; wherein the channel is defined within the migration medium by a rapidly cured de-wicking ink and is defined at the surface of the first and second major planes of the migration medium by first and second impermeable lamination media; and wherein at least one of the impermeable media is transparent such that a change in color or brightness can be determined, as between a trigger area of the migration path and a distal portion of the migration channel.
US Pat. Application No. 20130287059 discloses a dosimeter comprising a wick in contact with a separate reservoir containing a mix of a colored dye, a wax and an amorphous polymer to indicate a distinct temperature range when the mix melts. The wicks are preferably made of porous paper with a pore size around 8 microns to allow for proper capillary action along its length. An adhesive, except where each wick contacts its respective reservoir and at a vent, preferably seals each wick.
In known art moving boundary indicating devices, the stationary phase (SP) is a porous material, such as paper and the mobile phase (MP) is a liquid. MP in these devices is a liquid and hence the movement of the boundary is fast and the maximum service life is short, e.g., maximum of about a couple weeks at room temperature. The known devices are difficult to make as a special construction of the liquid reservoir is required and devices require sealing, usually heat sealed at the edges to control the movement of the liquid. It is also difficult to make small, e.g., smaller than a centimeter devices. In the known moving boundary devices, the mobile phase moves as a liquid and not as a vapor. There is no report on indicating devices based on diffusion of vapor of a MP (e.g., vapor of a solid compound which sublimes) through a non-porous polymeric SP.
Thus there remains a need for moving boundary devices that have longer lifetimes, are easier to make and have improved reliability.